1. Field of the Invention
This invention relates to the field of image data compression. More particularly, this invention relates to image data compression utilising frequency separation and entropy encoding.
2. Description of the Prior Art
British Published Patent Application GB-A-2 251 756 (Sony Broadcast & Communications Limited) describes a system using sub-band frequency separation and entropy encoding as part of a data compression process. Sub band frequency separation is used to decorrelate the video data into spatial frequency bands of uniform size within the two-dimensional spatial frequency domain. Spatial frequency component data within these bands is then subject to entropy encoding to bring about data compression.
Another video data compression system is described in IEEE Transactions on Circuits and Systems for Video Technology, Volume 1, No. 2, June 1991, pages 174 to 183, "Sub band Coding Algorithms for Video Application: Videophone to HDTV-Conferencing" by Hamid Gharavi. In contrast to the above, a video compression system is described which separates the data into sub band components in the two-dimensional spatial frequency domain of non-uniform size. This form of frequency separation is known as "logarithmic" or "wavelet" coding.